PHYSICAL MODELING OF NATURAL VENTILATION THROUGH SCREENS AND WINDOWS IN GREENHOUSES

An experimental and theoretical study of air exchange through porous s creens and window openings in greenhouses was conducted in order to ch aracterize the influence of the resistance of porous screens and windo w openings on airlow and to characterize wind velocities and air tempe rature differences which derive these flows. Fluctuations in wind velo city were related to the mean wind velocity through a parameter which is evaluated based on a power spectrum analysis. In turn, wind pressur e was related to this mean wind velocity such that the turbulence was taken into account. The relationship between air exchange through poro us screens or window openings and the driving potential was studied ba sed on an approach derived from fluid mechanics. The predictions made of airflow versus wind pressure and temperature differences agree reas onably well with experimental data, differences between them being les s than 20%, in general. (C) 1998 Silsoe Research Institute.